Oxidative gas phase carbonylation of methanol to dimethyl carbonate over chloride-free Cu-impregnated zeolite Y catalysts at elevated pressure

Abstract

Incipient wetness impregnation of zeolite Y with copper(II) nitrate solution and inert activation at 650°C led to active catalysts for the oxidative carbonylation of methanol to dimethyl carbonate in the gas phase. Activities were measured under elevated pressure (0.4–1.6MPa) with feed compositions of CO/MeOH/O2=40/20/6–1.5vol.% (balanced by N2) over zeolite Y loaded with 10–17wt.% copper. It could be shown that inert activation at 650°C enhanced the activity, and that Cu loading of 14–17wt.% gave the best performance. By combined XRD, TEM, TPR and DRIFT characterization it was found that the inert activation initiated dispersion of crystalline CuO, auto-reduction of Cu2+ to Cu+ and redistribution of copper ions with enrichment inside the supercages of the zeolite. The O2 content of the feed was found to control the selectivity to dimethyl carbonate. Dimethyl carbonate selectivities of 70–75% were achieved within the temperature range of 140–170°C at an O2 content of 1.5vol.%. This allowed space-time yields of dimethyl carbonate up to 632glcat−1h−1 at methanol conversions of 5–12%. Formation of the main side product, dimethoxymethane, was surprisingly affected by CO, which is not in line with suggested reaction pathways. A mechanism is proposed including formation of surface carbonate structures as common intermediate.